The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Electrical printed circuit boards (PCB) are well known in the art. Generally PCBs comprise an insulating substrate that is glued to a thin layer of conductive metal. The insulating substrate is chosen from a number of materials such as fiberboard, fiberglass, flexible polyamide and the like. The choice of substrate material is generally dictated by temperature specifications, cost, and need for mechanical flexibility such as bending.
The conductive metal is generally copper however other metals can also be used depending on the situation. An etching mask is applied to the conductive metal and defines the shape of the circuit traces that will be formed on the PCB. An etching solution then dissolves away the portions of the conductive metal that are not protected by the etching mask. When the etching mask is removed the desired circuit traces are all that remain of the conductive metal.
Some applications demand that the metal be resistant to corrosion and wear. In those cases it is common to plate the copper with nickel and gold, however such a coating is undesirably expensive.
Referring now to FIG. 1, a cross section is shown of a typical PCB 10 of the prior art. PCB 10 includes a substrate 12. Circuit traces 14-1, 14-2, and 14-3, collectively referred to as circuit traces 14, are formed as described above. In this example a pushbutton switch 16 is also shown attached to PCB 10. Pushbutton switch 16 includes a pliable body 18 and a conductive pill 20. A user can press the top of switch 16 such that pliable body 18 deforms and allows conductive pill 20 to make a circuit between circuit traces 14-1 and 14-2. When the user releases button 16 pliable body 18 returns to its original shape and the circuit is reopened. Such a combination of PCB 10 and switch 16 are commonly used in keypads for devices such a cell phones, automobile radios, and the like.
An undesirable characteristic of PCB 10 is that an extra expense in incurred if circuit traces 14-1 and 14-2 need to be coated with nickel/gold to increase the durability and/or current carrying capacity in combination with switch 16. The extra expense comes by virtue of having to also coat circuit trace 14-3 along with circuit traces 14-1 and 14-2. It is impractical to coat a subset of traces 14. Instead it is more simple to coat all traces 14 simultaneously.